1. Field of the Invention
The present invention pertains to flexible cellular polyurethane foam compositions which are permanently flame-retardant, and to methods for the preparation thereof. More particularly, the present invention relates to the preparation of essentially open-celled, or reticulated, flexible, cellular, permanently flame-retardant, polyurethane foam compositions by an in situ one-step process, utilizing tribromoneopentyl alcohol as the flame-retardant.
2. Prior Art
It is known in the art to make flame-retardant polyurethane foams by various means, and although some degree of commercial success has been attained, none of the known materials is entirely satisfactory. In addition to the shortcomings of the known methods and products, new uses for polyurethane foams are being continually developed, in some of which flame retardancy is a required property. Further, due to increased public awareness of the dangers from fire inherent in many common materials (including, but by no means limited to, polyurethane foams) used as components of clothing, furniture, buildings, vehicles, packing materials, electrical appliances, and so on, stricter regulations, controls, and specifications are constantly being imposed with respect to polyurethane foams used in older and well-established applications.
The art generally recognizes that rigid polyurethane foams are relatively easier to render flame-retardant than are flexible polyurethane foams, and that reticulated flexible polyurethane foams are particularly difficult to produce with permanent flame-retardancy. Rigid polyurethane foams are generally closed-cell foams, and are thus inherently more flame-retardant than the open-cell flexible polyurethane foams which are the subject of the present invention. In the open-cell foams, every open and interconnecting cell acts as a chimney so that such products burn readily unless treated with a flame-retardant. In addition, the predominantly closed-cell rigid polyurethane foams are generally made with a halogenated hydrocarbon, especially a fluorocarbon, blowing agent which is retained within the cells. This retained halogenated blowing agent imparts some flame-retardancy to the foam. In contrast to this, the open-cell foams contain air within the cell structure, which favors burning unless the foam is treated with a flame-retardant.
The known methods of achieving some degree of flame-retardancy in polyurethane foam compositions include incorporating into the reaction mix prior to foaming such chemicals as antimony oxide, inorganic phosphates, phosphate esters, halogenated phosphate esters, organic phosphonates, halogenated organic phosphonates, halogenated hydrocarbons, elemental phosphorus, and various others. It is also known to impart some degree of flame-retardancy to flexible polyurethane foams by an after-treatment of the cured foam, such as by impregnation or coating with a flame-retardant chemical or chemical composition. Another known means is to utilize, as reactants to forming urethane foams, halogenated polyols as well as polymerized diisocyanates.
The prior art methods for making flame-retardant flexible open-cell polyurethane foams are two-step or three-step processes, entailing making flame-retardant foams and then reticulating them in a separate step; or making foams without a flame retardant, reticulating them in a second step and then rendering them flame-retardant by means of a third, post-treatment step. These multi-step processes increase cost, and do not provide foams which are permanently flame-retardant.
As examples of prior art methods and compositions, the use of halogenated phosphate esters is disclosed in U.S. Pat. No. 3,793,240 and U.S. Pat. No. 3,872,053; the combination of ammonium phosphate and halogenated phosphate esters is disclosed in U.S. Pat. No. 3,795,637; the use of phosphonates is disclosed in U.S. Pat. No. 3,737,397; the use of halogenated hydrocarbon polymers and optionally, chlorinated paraffin is disclosed in U.S. Pat. No. 3,810,851; the use of chlorinated paraffin and antimony oxide is disclosed in U.S. Pat. No. 3,799,897; the use of halogenated aromatic amines is disclosed in U.S. Pat. No. 3,738,947; the use of a combination of monoammonium phosphate and amino-poly-imidazolineamide is disclosed in U.S. Pat. No. 3,803,063; the use of inorganic salts, oxides, and hydroxides is disclosed in U.S. Pat. No. 3,737,400; the use of brominated benzoquinone is disclosed in U.S. Pat. No. 3,725,316; the use of fumaric acid is disclosed in U.S. Pat. No. 3,746,664; the use of combinations of halogenated hydrocarbons, organic or inorganic phosphorus compounds, and "inert" fillers such as antimony oxide is disclosed in U.S. Pat. No. 3,826,762; the use of azodicarbonamide is disclosed in U.S. Pat. No. 3,826,764; the use of phosphonated and halogenated polyether polyols is disclosed in U.S. Pat. No. 3,741,919; the use of U.S. Pat. No. 3,732,265; and U.S. Pat. No. 3,773,696; the use of a combination of polybrominated diols and chlorinated hydrocarbon polymers is disclosed in U.S. Pat. No. 3,738,953; and the use of polymers of tolylene diisocyanate in combination with halogenated aliphatic phosphate esters is disclosed in U.S. Pat. No. 3,803,064.
As previously mentioned, the known methods, especially those claimed to be useful for flexible polyurethane foams, have drawbacks which keep them from being completely satisfactory. Many of the proposed flame-retardant chemicals upset the surface chemistry of the foaming system leading to the formation of coarse cells, uneven distribution of cell size, and even cause collapse of the rising foam. This is particularly so in the manufacture of flexible open-celled foams by in situ processes, these processes requiring a delicate balance of surface-active chemicals to produce open cells without foam collapse.
Additives which are not chemically bound into the urethane polymer are prone to loss during aging and use due to extraction by water and/or organic solvents, by volatilization, and by leaching into other substrates in contact with the cured foam. Some of these known additives act as plasticizers and thus have adverse effects on the physical properties of the foam, such as loss of tensile strength, compression set, and load-bearing capacity. Some are expensive; and some, although effective in increasing flame-retardance, add dead weight to the foam and increase its density. This is an additional economic disadvantage since no increase in foam volume is obtained, and in most cases the foam is sold by volume rather than by weight.
Among the halogenated additives, such as the halogenated phosphate esters, those containing bromine are generally much more effective per unit weight as flame-retardants than those containing chlorine. However, there are off-setting disadvantages; the brominated products are more costly, and in some cases they cause scorch and discoloration of the foam during curing. If chlorinated phosphates are employed to avoid these disadvantages, higher concentrations are needed for a equivalent degree of flame-retardance. This results in some compromise of the cost advantage, and in an increase of some of the undesirable other side effects previously discussed.
Although the known reactive flame-retardants become bound to the urethane polymer and thus are not readily removed by volatilization, extraction, and migration, they also have serious disadvantages, including undesirable effects on polymer structure and hence on physical properties, and on the surface chemistry of cell formation.
The present invention is directed to overcoming the foregoing problems, in the in situ manufacture of flexible reticulated polyurethane foam.